1. Field of the Invention
The present invention relates an apparatus for inputting thereinto image information, and more specifically, to an image sensor for converting optical image information into an electric signal.
2. Description of the Related Art
Known examples of conventional image sensors include an image sensor having a structure of FIG. 8, which is disclosed in JP-A-01-298863. In this image sensor, output terminals of a plurality of photoelectric converting elements 111, 112, . . . , 11n, which photoelectrically convert image information into electric signals are connected to input terminals of readout switching elements 121, 122, . . . 12n. Control terminals of the respective readout switching elements 121, 122, . . . 12n are connected to a scanning circuit array 103, and output terminals of the respective readout switching elements 121, 122, . . . , 12n are connected to a first common line 132.
The common line 132 is connected to a first input terminal of a switching element B107, an input terminal of a control circuit 106 is connected to a control terminal of the switching element B107, and an output terminal of the switching element B107 is connected to an image signal output terminal 102.
In the scanning circuit array 103, “n” stages of flip-flops are connected to each other in series so as to be arranged as a shift register, and the readout switching elements 121, 122, . . . , 12n are sequentially brought into ON states in response to pulses which are entered from an operating pulse input terminal 109 in a time sequential manner.
As a result, photoelectrically-converted image signals which are inputted from the photoelectric converting elements 111, 112, . . . , 11n are sequentially synchronized with the pulses and outputted via the switching element B107 from the image signal output terminal 102.
However, as shown in the structure described in the above-described conventional technique, in the case where output signals of the photoelectric converting elements 111, 112, . . . , 11n are directly read out, as represented by “Y” in the drawing, electric charges stored in the photoelectric converting elements 111, 112, . . . , 11n by illuminated light amounts (corresponding to brightness levels) are discharged by the switching element B107, and discharged waveforms (image signals) from the photoelectric converting elements 111, 112, . . . , 11n are rounded due to wiring capacitances present on a mounting board, or load capacitances of externally-connected circuits, so these discharge waveforms become triangular shapes.
As a consequence, the above-explained image sensor owns a drawback in that while the image sensor cannot acquire the waveforms as flat waveforms, for example, even when signals have the same brightness levels, potentials at vertexes of triangular waves are fluctuated, so the above-described conventional image sensor cannot acquire the signal waveforms in high precision.